Who's on hydra?

excerpt.ssh.config

Host hydra*
  Hostname %h.eecs.utk.edu
  User <netid>
  ForwardX11 yes
  forwardagent no

oneliner.sh

# note: dis is expanding using ZSH
# if you don't have the timeout command, just remove `timeout 2s ` from the command
# you should have yer ssh key set up
for i in {0..30};do timeout 2s ssh hydra${i} -o ConnectTimeout=1 -o ConnectionAttempts=1 -o PasswordAuthentication=no users | xargs echo users on hydra${i}: ;done

whosonhydra.sh

#!/bin/bash

TMPDIR=/tmp/hydrausers
TIMEOUT=10
DEBUGLOG=${TMPDIR}/debug.log
FAILURE=0

mkdir -p $TMPDIR
touch $DEBUGLOG
declare -g -A failures
declare -g -A hydrausers

ssh hydra0 echo
hydralist=$(echo hydra{0..30})

# get all whos and put them into /tmp/hydrausers
function gethydras() {
  rm /tmp/hydrausers/hydra* 2>&1 >/dev/null
  parallel-ssh -i -t $TIMEOUT -o /tmp/hydrausers -H "${hydralist}" \
    'users' > $DEBUGLOG
  FAILURE+=$(grep 'FAILURE' $DEBUGLOG | wc -l)
  while read -r failedhost; do
    # skip nothing, literally
    if [[ $failedhost == "" ]]; then continue; fi
    echo '!FAILURE' > $TMPDIR/$failedhost
  done <<< $(grep 'FAILURE' $DEBUGLOG | cut -d' ' -f4 )
  # failures+=( ["$(grep 'FAILURE' $DEBUGLOG | cut -d' ' -f4)"]="$(grep 'FAILURE' $DEBUGLOG )" )
}

gethydras

for i in {0..30}; do
  users=$(cat $TMPDIR/hydra$i )
  if [[ $users == '!FAILURE' ]]; then
    # rip
    failures+=( ["hydra$i"]="$(cat $DEBUGLOG | grep hydra$i )" )
  else
    hydrausers+=( ["hydra$i"]="$(cat $TMPDIR/hydra$i )")
  fi
done

for i in {0..30}; do
  echo hydra$i: $(echo ${hydrausers[hydra$i]} | wc -w) users: ${hydrausers[hydra$i]}
done

for key in ${!failures[@]}; do
    echo ${key} ${failures[${key}]}
done

# Total number of unique users:
cat /tmp/hydrausers/hydra* | grep -v '!FAIL' | tr ' ' '\n' | sort | uniq | wc -l | xargs echo 'total users:'